A new analysis suggests there's been a huge increase in the number of U.S. children diagnosed with bipolar disorder, but experts question whether the surge is real and say some kids have been mislabeled.

Researchers looked at the number of times children under 19 went to the doctor and were diagnosed with bipolar disorder, also known as manic depression. They found a 40-fold increase, from an estimated 20,000 visits in 1994 to 800,000 in 2003. The jump coincided with children's rising use of antipsychotic medicine.

The numbers echo other estimates suggesting as many as 1 million U.S. children are bipolar, but it remains a controversial diagnosis in children. That's partly because their symptoms often differ from adults', and because most powerful antipsychotic drugs used to treat bipolar disorder were approved for adults and have not been well-studied in children.

Some doctors believe bipolar disorder doesn't occur in children, and until last month there was only one drug approved to treat the illness in kids.

The study's lead author, Dr. Mark Olfson of Columbia University and the New York State Psychiatric Institute, said the results likely reflect over-diagnosis now or under-diagnosis in the past, rather than a true increase. Olfson has received speaking fees from Janssen LP, which makes one of the pediatric bipolar drugs, and has consulted for other makers of psychiatric drugs.

Dr. Sharon Hirsch, a University of Chicago psychiatrist, said that while she is treating increasing numbers of bipolar children, she doubts there's a 'vast epidemic.'

More public awareness about mental illness, spurred partly by heavy marketing of psychiatric drugs, could have contributed to the surge. And early in the study, a leading manual of psychiatric illnesses expanded criteria for diagnosing bipolar disorder, Olfson noted.

Symptoms include extreme mood swings and disruptive behavior. In children, extreme irritability is sometimes the main symptom.

It affects more than 5 million adults. The causes are uncertain but the disorder tends to run in families.

Dr. David Fassler, a University of Vermont psychiatry professor, said research suggests that close to half of children thought to be bipolar may be misdiagnosed. He said parents should get a second opinion if they have concerns about a diagnosis or proposed treatment.

'Bipolar disorder is not always easy to recognize in children and adolescents. There's considerable overlap with other conditions, including ADHD, conduct disorder, anxiety disorders and depression,' said Fassler, who was not involved in Olfson's study.

Dr. Thomas Insel, director of the National Institute of Mental Health, which partially funded the research, said the study 'waves a flag saying we've got to do much, much better in finding ways to validate psychiatric diagnoses in children. This is an area that really needs hard science.'

The study appears in the September issue of Archives of General Psychiatry.

It follows a report showing a big increase in U.S. children hospitalized with bipolar disorder, from 1.3 per 10,000 in 1996 to 7.3 per 10,000 in 2004, published in June in the journal Biological Psychiatry.

Olfson and colleagues analyzed annual surveys of outpatient visits from the National Center for Health Statistics. Adult visits for bipolar disorder also increased during the study but not as markedly.

Charlie Crow, 13, of Verona, N.J., who was diagnosed with bipolar disorder in 2001, said the results don't surprise him because he knows lots of other kids who are bipolar. When he was first diagnosed at age 7, though, he felt alone and isolated.

He said it helps to know there are other kids like him.

'They know how I feel and I know how they feel,' he said.

His mother, Susan Montanile, said Charlie was a precocious, disobedient and moody 3-year-old. He later had vivid, violent nightmares and violent outbursts in school.

'He would cycle even within 10 minutes, from hysterical giddiness and laughter watching TV' to screaming when she called him for dinner.

It was 'like walking on eggshells,' she said. 'You never really knew within a given hour what was going to happen.'

Psychiatric medicine has helped, but has also caused weight gain, drowsiness and other side effects.

Montanile worries that the new study might embolden skeptics who blame 'bad parenting' and think afflicted children are simply misdiagnosed brats.

A generation ago, bipolar kids were likely mislabeled as simply truants or troublemakers, said Christine Walker, of Winnetka, Ill., whose 7-year-old son, Schuyler, was diagnosed a few years ago.

'This has always existed,' Walker said. 'It just didn't have a name, it didn't have a face.'